-LRB- CNN -RRB- -- President Abraham Lincoln and his wife , Mary Todd , needed a baby-sitter .

It was April 18 , 1864 , and the Lincolns had planned to go to a fair in Baltimore , returning the next day . They needed someone to watch their 11-year-old son , Tad .

A newly published letter from Mrs. Lincoln requesting a sitter gives rare insight into the family 's life inside the Lincoln White House , showing one way the family had to juggle their busy schedules , just like everyone else .

The letter is being offered for sale by the Raab Collection , a dealer in historical documents , valued at $ 15,000 .

It 's not long -- just one line -- but the signed letter is in the first lady 's hand .

`` Hon. Mr. Harrington , We would like to have the services of Charles from today , at 2 P.M. until tomorrow at 11 A.M. Very Resp . Mrs. Lincoln . ''

`` Charles '' was Charles Forbes , a Treasury Department employee who was detailed to the Lincolns and often served as the president 's valet , footman , messenger or attendant , according to the Raab Collection .

George Harrington was assistant secretary of the Treasury and Forbes ' boss and handled personal financial matters for the Lincolns .

`` Children in the White House have always held a great fascination with the American people , '' said Nathan Raab , vice president of the Raab Collection . `` It shows the president and first lady at their most personal , their most human . ''

Mary Todd Lincoln ended up not going to the Baltimore event , likely too burdened with preparations for a reception the next night , the final White House reception of the season , Raab says .

Forbes ' close family relationship soured a year later when President Lincoln was assassinated . Forbes was seated outside the president 's box at Ford 's Theatre and was the one who allowed the assassin , John Wilkes Booth , to enter . Forbes and the president 's guard then left for a drink , leaving Lincoln unattended , Raab says .

Mary Todd Lincoln ended up blaming Forbes for her husband 's death .

`` Lincoln , '' a film about the 16th president and his battle to end slavery , is up for 12 Academy Awards this year , including best picture . The ceremony is scheduled to be broadcast Sunday night .

@highlight

Mary Todd Lincoln requests a baby-sitter in the 1864 letter

@highlight

She needed someone to watch their 11-year-old son , Tad

@highlight

The letter is being offered for sale , valued at $ 15,000